From DE 1 174 113 B1, an axial cage forming the class for an axial needle bearing is known that substantially is formed of a thin-walled washer with a W-shaped profile cross section, the individual profile legs of which are formed by an inner radial rim formed on the inner edge of the washer, an outer radial rim formed on the outer edge of the washer and a U-shaped center crimp connected by way of inner and outer axial profile sections to the radial rims and having the same radial extent as the rims. A number of evenly spaced rectangular cage pockets are cut from the center crimp and the adjacent axial profile sections, between which pockets an equal number of pocket connecting pieces are formed connecting the rims with one another, by means of which connecting pieces the rolling bodies formed as bearing needles are retained in the cage pockets and are also guided in the circumferential direction.
From practice it has been known for a long time that, during bearing operation, such axial cages cause so-called needle drilling due to the centrifugal forces acting on the bearing needles, in which the bearing needles come into frictional contact with their outer end faces on the outer corner radii of their cage pockets. This friction contact has the effect that the corner radii provided at these locations for reasons of increasing the shear strength and dimensional accuracy of the axial cage little by little are machined or worn away and it finally results in fracture or premature failure of the axial cage.
To prevent such a premature failure of the axial cage caused by needle drilling, it was proposed by DE 101 43 089 A1 to form the axial cage so that the axial cage has, at the transition area of the inner and/or the outer radial rim to the adjacent axial profile section, a circumferential bulging that transitions at the free profile end of the radial rim into a circumferential necking. This circumferential necking projects in the axial direction into the cage pockets and is in supporting contact with the end faces of the bearing needles via two contact points such that the bearing needles can no longer contact the corner radii of the cage pockets due to the influence of centrifugal forces.
In this very advantageous solution, however, it has been shown that it can be realized in terms of production only with additional expense or with completely changed processing methods. The typical processing method for producing a non-metal-cut axial cage includes, in a known way, producing this cage from an endless sheet metal strip in multiple processing steps in a stepped punching-drawing tool in which, at first, a washer connected to the sheet metal strip by way of two lateral retaining connecting pieces is punched, then the U-shaped crimp and the outer radial rim is formed into the washer, then the inner diameter of the axial cage is punched and the inner radial rim is formed on the washer, then the cage pockets are punched, and finally the outer diameter of the cage pockets is punched. At the end of the individual processing steps, the finished axial cage is still connected to the sheet metal strip merely by way of the lateral retaining connecting pieces and it is separated from this strip in a final processing step. However, if this rim has, as in the described solution, a circumferential necking that transitions into a circumferential bulging, then this separation of the finished axial cage from the lateral retaining connecting pieces is not directly possible at the rim due to the bulging arranged under the retaining connecting pieces, because otherwise this bulging would be damaged. The separation of the axial cage from the retaining connecting pieces must be realized at the inner edge of the sheet metal strip, so that the retaining connecting pieces at first remain on the separated axial cage and then must be removed with great expense using separate tools. Another possibility for creating the described axial cage would be to produce these from individual sheet metal blanks, but such a production would require expensive transport devices that transport the sheet metal blanks from one processing step to the next and thus would disadvantageously increase the costs for the production method.
Another possibility of preventing the described disadvantageous needle drilling in an axial cage was also disclosed by EP 2 103 825 A1. That publication proposes an axial cage that likewise has a U-shaped center crimp with adjacent axial profile sections, but the radial profile sections adjacent to these axial profile sections are not formed as inner and outer rims of the axial cage, but instead transition at the height of the roll axes of the bearing needles into additional inner and outer axial profile sections on which the rims extending in the opposite radial direction toward the U-shaped center crimp are formed. In this axial cage, the cage pockets extend from the outer axial profile cross section by way of the U-shaped center crimp to the inner axial profile cross section, wherein, on the outer and inner axial profile sections, within the cage pockets, two wedge-shaped sheet metal tabs are formed on the rim side, wherein these tabs come into point-wise supporting contact with the end faces of the bearing needles at the height of their roll axes due to the effect of centrifugal forces on the bearing needles.
Such a solution has also proven to be disadvantageous to the extent that the wedge-shaped sheet metal tables are arranged on additional inner and outer axial profile sections that must be formed in the axial cage and these additional axial profile sections require, in addition to increased production expense for the axial cage, also an increased axial installation space for the axial cage that in many cases is not available. In addition, the U-shaped center crimp extending radially past the inner and outer axial profile sections due to the special profiling of the axial cage in the pocket connecting pieces likewise causes production-related problems, because such axial cages are typically collected in bins after separation from the sheet metal strip for transport to their final processing. However, due to the U-shaped crimp freely projecting away from the inner and outer axial profile sections in the not-yet deburred pocket connected pieces, there is the risk that the axial cages will become hooked in each other with their pocket connecting pieces in the bins. To ensure correct and reliable further processing of the axial cages, this can be prevented only with additional stacking devices, which similarly contribute to increasing the production costs of such axial cages.